In recent years, wireless networks have emerged as flexible and cost-effective alternatives to conventional wired local area networks (LANs). At the office and in the home, people are gravitating toward use of laptops and handheld devices that they can carry with them while they do their jobs or move from the living room to the bedroom. This has led industry manufacturers to view wireless technologies as an attractive alternative to Ethernet-type LANs for home and office consumer electronics devices, such as laptop computers, Digital Versatile Disk (“DVD”) players, television sets, and other media devices. Furthermore, because wireless networks obviate the need for physical wires, they can be installed relatively easily.
Wireless communication systems adapted for use in homes and office buildings typically include an access point coupled to an interactive data network (e.g., Internet) through a high-speed connection, such as a digital subscriber line (DSL) or cable modem. The access point is usually configured to have sufficient signal strength to transmit data to and receive data from remote terminals or client devices located throughout the building. For example, a portable computer in a house may include a PCMCIA card with a wireless transceiver that allows it to receive and transmit data via the access point. Data exchanged between wireless client devices and access points is generally sent in packet format. Data packets may carry information such as source address, destination address, synchronization bits, data, error correcting codes, etc.
A variety of wireless communication protocols for transmitting packets of information between wireless devices and access points have been adopted throughout the world. For example, in the United States, IEEE specification 802.11 and the Bluetooth wireless protocol have been widely used for industrial applications. IEEE specification 802.11, and Industrial, Scientific, and Medical (ISM) band networking protocols typically operate in the 2.4 GHz or 5 GHz frequency bands. In Europe, a standard known as HIPERLAN is widely used. The Wireless Asynchronous Transfer Mode (WATM) standard is another protocol under development. This latter standard defines the format of a transmission frame, within which control and data transfer functions can take place. The format and length of transmission frames may be fixed or dynamically variable.
Although traditional wireless networks work fairly well for residential Internet traffic running at data rates below 1 megabit per second (Mbps), transmission of high-bandwidth video programs is more problematic due to the much faster video data rates. High-bandwidth data transmissions can be degraded by the presence of structural obstacles (e.g., walls, floors, concrete, multiple stories, etc.), large appliances (e.g., refrigerator, oven, furnace, etc.), human traffic, conflicting devices (e.g., wireless phones, microwave ovens, neighboring networks, X10 cameras, etc.), as well as by the physical distance between the access point and the mobile terminal or other device. By way of example, an IEEE 802.11b compliant wireless transceiver may have a specified data rate of 11.0 megabits per second (Mbps), but the presence of walls in the transmission path can cause the effective data rate to drop to about 1.0 Mbps or less. Degradation of the video signal can also lead to repeated transmission re-tries, causing the video image to appear choppy. These practical limitations make present-day wireless technologies one of the most unreliable of all the networking options available for home media networks.
One proposed solution to this problem is to increase the number of access points in the home, with the various access points being interconnected by a high-speed cable wire. The drawback of this approach, however, is that it requires that cable wires be routed through the interior of the structure.
An alternative solution is to utilize wireless repeaters to extend coverage of the network throughout the building. For example, D-Link Systems, Inc., of Irvine, Calif. manufactures a 2.4 GHz wireless product that can be configured to perform either as a wireless access point, as a point-to-point bridge with another access point, as a point-to-multi-point wireless bridge, as a wireless client, or as a wireless repeater. As a wireless repeater, the product functions to retransmit packets received from a primary access point. But the problem with these types of wireless repeaters is that they retransmit at the same frequency as the primary access point device. Consequently, because the primary access point and repeaters share the same channel, the bandwidth of the network is effectively reduced for each repeater installed. For example, if a data packet needs to be repeated (i.e., retransmitted) three times in the same channel, each packet must wait until the previous packet has been repeated which means that the resulting bandwidth loss is 67%. So if the initial video transmission starts out at, say, 21 Mbps, the effective payload data rate at the receiver end is diminished to about 7 Mbps. Naturally, with more repeaters, more data hops are required, so the bandwidth loss becomes worse. This approach basically trades-off bandwidth for signal range—extending the range of the wireless network, but sacrificing valuable bandwidth in the process.
Still another attempted solution to the problem of wireless transmission of video data is to lower the bandwidth of the video through data compression. This technique involves compressing the video data prior to transmission, then decompressing the data after it has been received. The main drawback with compression/decompression techniques is that they tend to compromise the quality of the video image, which is unacceptable to most viewers. This approach also suffers from the problem of lost connections during transmission.
In view of the aforementioned shortcomings, there exists a strong need for a highly reliable wireless network (e.g., on a par with coaxial cable) that provides very high data rates (e.g., 30 Mbps) throughout the full coverage range of a home or building.